Illumination systems are an important aspect of industrial, residential, commercial, and architectural design and cover a wide variety of cost and technical considerations. Most conventional illumination systems are considered to be either direct, indirect, or direct-indirect illumination.
In the case of direct illumination systems, the illumination source (e.g., downlights) is often visible, which often presents disadvantages such as significant amounts of glare, high surface brightness, and the like. To mitigate these disadvantages, shielding elements such as baffles or lenses are typically used to cover or substantially surround the lighting source, e.g., a fluorescent lamp. However, shielding elements do not completely eliminate these disadvantages. Shielding elements also fail to produce optimal optical efficiency, particularly in areas where the surfaces of the lamps are not directly viewed.
Indirect illumination systems are typically used to mitigate many of the disadvantages associated with direct illumination, a few of which were noted above. In indirect illumination systems, the illumination source (e.g., uplights) is mounted below a troffer such that light is reflected (indirectly) towards an area to be illuminated. While indirect illumination systems avoid some of the disadvantages associated with direct illumination systems, they introduce a substantial loss in the luminous flux or lumens reflected, and are therefore significantly less efficient than direct illumination systems.
In direct-indirect illumination systems, both direct illumination lamps and indirect illumination lamps are used. While the direct-indirect illumination systems offer some improvements in transmitted lumens when compared to indirect illumination systems, they still introduce many of the disadvantages associated with direct illumination systems.
Other conventional illumination systems, such as parabolic and prismatic troffers, also have shortcomings. For example, parabolic and prismatic troffers often introduce distractions related to inconsistent brightness and lighting patterns, particularly to moving observers. Additionally, prismatic troffers often suffer from reduced lighting efficiency and the “cave effect”, where the upper walls of the illuminated area are dark.
Lighting system efficiencies are an important consideration during the lighting system design process. During design, the choice of a particular illumination source will depend largely on the design objectives, the technical requirements of the particular application, and economic considerations. Other design factors include illumination source distribution characteristics, lumen package, aesthetic appearance, maintenance, productivity, and the lighting source.
The lighting source can be one of the most important considerations. Known lighting sources include, for example, incandescent bulbs, fluorescent bulbs or lamps, and more recently solid state lighting sources, such as light emitting diodes (LEDs).
Incandescent bulbs, however, are notoriously energy inefficient with approximately ninety percent (90%) of the electricity consumed by the bulb being released as heat rather than light. Fluorescent lamps are substantially more energy efficient (by a factor of about ten) than incandescent bulbs. Therefore, fluorescent lamps are most often the preference of lighting system designers, particularly for industrial and commercial applications. LEDs, however, are even more energy efficient than fluorescent lamps—emitting the same lumens as incandescent bulbs and fluorescent lamps using a fraction of the energy.
In addition to being more energy efficient, LEDs also provide a substantially longer operational life when compared to incandescent bulbs and fluorescent lamps. For example, the operational life of an LED is about 70,000 hours. By contrast, fluorescent lamps tend to last up to about 20,000 hours and incandescent bulbs are about 1000 hours. Other LED advantages include improved physical robustness, reduced size, and faster switching. Although they offer many advantages, LEDs are relatively expensive for use in lighting applications and require more current and heat management.
Although LEDs can be combined to produce mixed colors, conventional LEDs cannot produce white light from their active layers. White light can only be produced by combining other colors. Thus, the particular manner used by LEDs to produce white light can be an important factor when considering LEDs as a lighting source.
One traditional approach for configuring LEDs to produce white light is the use of multicolor light sources such as specular reflector systems. Another approach includes the use of multicolor phosphors or dyes. Each of these approaches, however, has significant deficiencies including the introduction of shadows, color separation, and/or poor color uniformity over the entire range of viewing angles. One solution to these deficiencies includes using a diffuser to scatter light from the various (i.e., multiple) sources. The use of a diffuser, however, or diffusive materials, can cause significant optical losses and can add significant expenses.
Given the aforementioned deficiencies, what is needed, therefore, is a low cost, optically efficient lighting system having desirable light distribution and luminance uniformity. What are also needed are simple, low cost systems and methods for controlling the light output distribution of a lighting source with minimal optical losses.